In black MS patients who have a history of optical neuritis there was a significant loss of 4.9 letters -- nearly a line of visual acuity -- when compared with white patients [95% CI minus 8.8-minus 1.0; (P=0.016)], reported Dorlan Kimbrough, MD, a post-doctoral fellow in neuroimmunology at Johns Hopkins University.

"There are several domains in multiple sclerosis that appear to be worse in African Americans," he said. "To my knowledge, this is the first study that quantitatively shows that vision and retinal structures are another domain that is worse in African Americans. We don't know the reasons for that yet. We don't know if it has to do with genetic factors or environmental factors."

The research team enrolled 830 individuals into the study, including 137 healthy controls and 693 patients diagnosed with MS at three sites, Johns Hopkins, the University of Pennsylvania in Philadelphia, and the University of Texas Southwestern in Dallas. Patients were recruited and observed from September 2008 through December 2012 and underwent serial optical coherence tomography scans and visual acuity testing during a 4-year period.

Patients self-identified as either African American or Caucasian American, and had relapsing remitting multiple sclerosis or secondary progressive multiple sclerosis. The study excluded individuals with diabetes, glaucoma, uncontrolled hypertension, major refractive errors, or other known eye disorders, Kimbrough said.

The control patients included 106 Caucasian Americans and 31 African Americans. The baseline age for the Caucasians was 32.5; the baseline age for the African Americans was 21.4 years. About 60% of the total cohort was women. The Caucasian controls were followed for about 2 years; the African Americans for 1.3 years.

"There were no clinically significant differences in visual acuity of healthy controls by race at any contrast level," Kimbrough observed. They were tested at contrast levels of 100%, 2.5% and 1%. The results were adjusted for age and sex.

About 88% of the MS patients were Caucasians; more than 75% were women; more than 90% had the relapsing/remitting form of multiple sclerosis. Median follow-up was 2 years.

The manifestations of MS in African Americans is more severe than in Caucasian Americans, Kimbrough said. "African Americans tend to have higher Expanded Disability Status Scale scores and higher multiple sclerosis severity scores at diagnosis," he said. "Markers of intrathecal immunoglobulin synthesis are seen more frequently and at higher levels than in Caucasians. Greater T1 and T2 lesion volumes are seen on MRI."

"I think [visual and retinal damage] is one of several things that doctors should be on the lookout for in African American patients," he said, including overall disability and difficulty in walking. "With this study we have added vision to the list. I think physicians should have more vigilance with African American patients with multiple sclerosis."

Margaret Burnett, MD, clinical professor of neurology and neuropathology at the University of Southern California in Los Angeles, told MedPage Today that "this information is compelling enough for doctors to look for these visual manifestations in African Americans with multiple sclerosis. They definitely should be looking for these symptoms."